New User Created Via Net.EXE

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 * Copyright 2025 Google LLC
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

rule new_user_created_via_net_exe {

  meta:
    author = "Endgame, JHasenbusch (adapted to Sigma for oscd.community)"
    description = "Identifies the creation of local users via the net.exe command"
    reference = "https://github.com/SigmaHQ/sigma/blob/master/rules/windows/process_creation/proc_creation_win_net_user_add.yml"
    license = "https://github.com/SigmaHQ/Detection-Rule-License/blob/main/LICENSE.Detection.Rules.md"
    rule_name = "New User Created Via Net.EXE"
    sigma_uuid = "cd219ff3-fa99-45d4-8380-a7d15116c6dc"
    sigma_status = "test"
    rule_id = "mr_c5c37a7b-d892-4592-a726-b0dbb45c1e55"
    tactic = "TA0003"
    technique = "T1136.001"
    type = "Detection"
    data_source = "Sysmon"
    platform = "Windows"
    severity = "Medium"
    priority = "Medium"
    false_positives = "Legitimate user creation. Better use event IDs for user creation rather than command line rules."

  events:
    $process.metadata.event_type = "PROCESS_LAUNCH"
    (
        re.regex($process.target.process.file.full_path, `net(|1)\.exe$`) nocase or
        $process.src.process.file.full_path = "net.exe" nocase or
        $process.src.process.file.full_path = "net1.exe" nocase
    )
    (
        strings.contains(strings.to_lower($process.target.process.command_line), "user") and
        strings.contains(strings.to_lower($process.target.process.command_line), "add")
    )
    $process.principal.hostname = $hostname

  match:
    $hostname over 5m

   outcome:
    //example usage of specifying test user and hostname to adjust risk score
    $risk_score = max(if($process.principal.user.userid = "user" and $process.principal.hostname = "hostname", 0, 15))
    $principal_process_pid = array_distinct($process.principal.process.pid)
    $principal_process_command_line = array_distinct($process.principal.process.command_line)
    $principal_process_file_sha256 = array_distinct($process.principal.process.file.sha256)
    $principal_process_file_full_path = array_distinct($process.principal.process.file.full_path)
    $principal_process_product_specfic_process_id = array_distinct($process.principal.process.product_specific_process_id)
    $principal_process_parent_process_product_specfic_process_id = array_distinct($process.principal.process.parent_process.product_specific_process_id)
    $target_process_pid = array_distinct($process.target.process.pid)
    $target_process_command_line = array_distinct($process.target.process.command_line)
    $target_process_file_sha256 = array_distinct($process.target.process.file.sha256)
    $target_process_file_full_path = array_distinct($process.target.process.file.full_path)
    $target_process_product_specfic_process_id = array_distinct($process.target.process.product_specific_process_id)
    $principal_user_userid = array_distinct($process.principal.user.userid)
    $log_type = array_distinct(strings.concat($process.metadata.log_type,"/",$process.metadata.product_event_type))

  condition:
    $process
}